We have shown that removal of the primary cortical input to the dentate gyrus triggers the growth of synapses by most remaining afferents and the creation of new functional circuitry. It is proposed that the new circuitry can perform much, if not all, of the function of the normal dentate. In order to evaluate this possibility, we will test the plasticity and the integrative properties of the various afferents singly and in combination by conventional electrophysiological analyses, as well as by a more comprehensive electrophysiological technique known as Wiener analysis. In addition, we shall employ current source density analysis to precisely and rigorously determine the organization of the new functional inputs on granule cell dendrites and discover if there are any changes in synaptic drive in afferents in the undeafferented zone and in interneurons. In order to analyze the mechanisms responsible for functional changes, we will analyze the emergent structure of the dentate. We will identify the sources for all new connections and determine their relative abundance. After regrowth has occurred, secondary lesions will be performed on all remaining extrinsic $ afferents in order to see if they are the source of all new synapses. Specific afferents will also be analyzed individually: commissural by secondary lesion, septal by histochemical methods using antibodies to ChAc, and interneurons by antibodies to GAD. We will also analyze the branching pattern of dendrites by a Golgi technique and the diameter of major dendritic branches by electron microscopy. From these structural data we hope to be able to reconstruct in entirety, the granule cell and its inputs after lesion. Also, during this next grant period we will continue our studies of axonal regeneration.